Pulverization process of a vulcanized rubber material

ABSTRACT

A process for producing a rubber powder from a vulcanized rubber material by the steps of: a) feeding a grinding device with the vulcanized rubber material; b) contacting the vulcanized rubber material with at least one liquid coolant; c) introducing at least one grinding aid additive into the grinding device; d) operating the grinding device so as to grind the vulcanized rubber material to form a rubber powder, and e) discharging the rubber powder from the extruder.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase application based onPCT/EP2003/011385, filed Oct. 14, 2003, which claims the priority ofEuropean Application No. PCT/EP02/13614, filed Dec. 2, 2002, the contentof both of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for producing a rubber powderfrom a vulcanized rubber material.

In particular, the present invention relates to a process forpulverizing a vulcanized rubber material by using a grinding device.

More in particular, the present invention relates to a process forpulverizing a vulcanized rubber material comprising a discarded rubbermaterial.

Even more in particular, the present invention relates to a process forpulverizing a vulcanized rubber material comprising a discarded rubbermaterial including discarded tyres previously torn to shreds.

2. Description of the Related Art

The increased production of industrial rubber products has resulted inthe accumulation of large amounts of rubber wastes which per se do notfind any practical applications and are generally disposed in dedicatedlandfills with the main drawbacks of environment pollution as well as ofthe need for large dedicated areas for storing said wastes.

Therefore, the reclaiming of vulcanized rubber material into a product,which can be advantageously reused, is a widely discussed issue and along-felt problem to be solved.

Used vulcanized rubber material, such as waste rubber, old tyres andindustrial rubber products, can be comminuted and added to rubbermixtures to be employed in a plurality of applications. This isparticularly advantageous since important amounts of used vulcanizedrubber material can be reused and, moreover, corresponding remarkableamounts of raw materials can be saved by replacing them with saiddiscarded material.

The use in a rubber composition of a comminuted vulcanized rubber, whoseparticle size generally does not exceed 500 μm, does not remarkablyimpair the quality of the final product.

However, according to the known technologies available on the market,fine powders can be obtained from rubber material at the expense oflarge amounts of energy.

Reclaiming processes of used rubber material which are currentlyemployed include: chemical reclaiming processes such as pyrolysis anddevulcanization; thermal reclaiming processes such as extrusion,injection moulding and pressure moulding; mechanical reclaimingprocesses such as granulation, densification, agglomeration andpulverization.

Document U.S. Pat. No. 4,090,670 discloses the recovery of rubber fromscrap vulcanized rubber tyres by devulcanization of the rubber tyres andsubsequent removal of the devulcanized material, e.g. by rasping. Thedevulcanization is obtained by raising the surface temperature of thevulcanized rubber material.

Document U.S. Pat. No. 4,968,463 discloses the reclamation ofthermoplastic material including the steps of: shredding to about onehundred millimiters, grinding to under about 40 millimeters, drying,pre-heating from 80° C. to 160° C., kneading at 120° C. to 250° C. andinjection moulding or extruding.

A method of pulverizing natural or synthetic rubber materials is known,for instance, from document U.S. Pat. No. 3,190,565 which discloses thecomminution thereof in mills provided with knife blades in the presenceof antiagglomerating agents (in the form of polyolefin fines) thatinhibit the sticking of the comminuted material to the cutting blades.

A further method of making powders from industrial rubbers consists incomminuting thereof by means of shear forces.

Document GB-1,424,768 discloses a plunger-type device provided with arotating member so that the rubber material is crushed in the minimalgap between the rotating member and the inside wall of said device.

Document U.S. Pat. No. 4,157,790 discloses a process for the productionof rubber powder having a particle size of from about 200 to 1,500 μm,said process comprising the step of providing small additions ofpowdering agents in order to obtain adequate fluidity of the rubberpowder. A carrier gas is used during size-reduction which is carriedout, for instance, by the grinding plates of a Pallmann mill. Theincrease in temperature which occurs in the size-reduction machine isminimized by cooling the carrier gas, e.g. at a temperature of about 5°C.

Document U.S. Pat. No. 4,650,126 discloses a process for grinding to aparticle size of less than about 1 mm in diameter a soft and tackypolymeric material in the presence of a grinding aid in an attritionmill having counter-rotating grinding elements adjustably spaced apart.The mill temperature is adjusted so that nearly all of the grinding aidis retained on the softened polymer particles, thus improving polymerflow and reducing to a minimum the amount of loose grinding aid to bedisposed of. Air is drawn through the mill to serve as the materialcarrier medium and at the same time to cool the mill, if required.

Document U.S. Pat. No. 2,412,586 relates to the fine grinding of rubberscrap with high grinding and screening efficiency. Said documentdiscloses a cyclic process in which the rubber stock, with preliminarychopping if necessary, is continuously fed to a grinding mill togetherwith a regulated amount of water and then subjected to the grindingoperation in the presence of the added water, the resulting ground stockpassed by a conveyer to a screen for screening out the fine particles,and the oversize material from the screen returned to the grinder forfurther grinding. According to said document the amount of waterrequired for most efficient grinding or screening varies somewhat withthe type of scrap being ground and with the fineness to which the scrapis to be ground.

A further method of producing finely dispersed powders from used rubbermaterials is the cryogenic destruction (e.g. Chemical Technology,Cryopulverizing, T. Nazy, R. Davis, 1976, 6, N° 3, pages 200-203).According to said method the rubber material is cooled to very lowtemperatures by using liquid nitrogen or solid carbon dioxide and thensubjecting the cooled material to impact or cutting. This methodproduces finely dispersed powders having particle dimensions less than500 μm, but it is very expensive due to the presence of a plantdedicated to liquid nitrogen production.

A further method of making powders from rubber materials consists inusing an extrusion device of the single-screw or multiple-screw type.

For instance, document U.S. Pat. No. 4,607,797 discloses thepulverization of used polymers in an extrusion apparatus wherein theused material is heated to above its melting temperature in a first zoneof said extrusion apparatus and cooled to below its solidificationtemperature with simultaneous pre-crushing and pulverizing of thesolidified material in a second zone of said apparatus to form apowdered material. The action of the screw of the extruder is used toconvey the material through the barrel of the extruder, whilepulverizing disks mounted on the screw in the second cooling zoneperform the pre-crushing and pulverizing of said material.

Document U.S. Pat. No. 5,743,471 discloses an extruder for solid stateshear extrusion pulverization of polymeric materials comprising a feedzone, a heating zone adjacent to the feed zone, a powder formation zoneadjacent to the heating zone and a powder discharge zone adjacent to thepowder formation zone. Furthermore, the extruder is provided withtemperature adjustment means for heating the polymeric material to atemperature lower than the decomposition temperature of the polymericmaterial in the heating zone and for maintaining the polymeric materialbelow its melting point in the powder formation zone, but at atemperature above its glass transition temperature in the powderformation zone to inhibit the formation of agglomerates.

Documents U.S. Pat. Nos. 4,607,796; 5,395,055; 5,704,555 and JP 6-179215disclose further processes according to which the extruder is providedwith heating and cooling zones.

SUMMARY OF THE INVENTION

The Applicant has perceived that, in processes for producing powdersfrom vulcanized rubber materials by using a grinding device, the controlof the temperature is essential to obtain high grinding yields in fineparticles which do not negatively affect the mechanical properties—e.g.tensile strength, elongation at break, abrasion resistance—of the rubbercompositions they are added to.

According to the present invention, the term “grinding device” is usedto indicate any machine which is suitable for carrying out thesize-reduction of a vulcanized rubber material by impact, cutting,tearing and/or shearing thereof. In order to increase the grinding yieldin fine particles, the Applicant has perceived that the rubber materialhas to be cooled so that during the grinding step the rubber particlesdo not stick and agglomerate.

Furthermore, the Applicant has perceived that a suitable control of therubber material temperature, i.e. a decrease thereof during the grindingstep, is particularly advantageous also in terms of energy to betransferred to the rubber material for the grinding thereof. In moredetails, the Applicant has perceived that, by controlling thetemperature of the rubber material, the mechanical energy which issupplied during the process can be used to give rise to shear stresseson the rubber particles so that an efficient grinding thereof isachieved. This means that said energy is not spent for carrying out thesoftening or melting of the rubber material and the devulcanizingthereof, but results in obtaining high grinding yields in very fineparticles of the rubber material.

Furthermore, the Applicant has perceived that, in order to perform avery efficient cooling of the rubber material, it is not sufficient toprovide the grinding device—e.g. the walls thereof—with a coolingcircuit which can remove a predetermined heat amount from the rubbermaterial by contacting the latter with the cooling circuit—e.g. with thecooled walls of the grinding device. In particular, the Applicant hasperceived that part of the heat produced during the grinding step has tobe removed by directly acting on the rubber material, i.e. by carryingout a cooling of the latter from the inside thereof.

The Applicant has further found that it is possible to efficiently coolthe rubber material by contacting the rubber material with a liquidcoolant.

According to the present invention, the term “liquid coolant” is used toindicate any coolant which is liquid at environmental temperature (i.e.at 20-25° C.) and at atmospheric pressure.

Preferably, the coolant is a liquid which at least partially evaporatesduring the grinding of the vulcanized rubber material so that at leastpart of the heat, which is produced during the grinding action, isdissipated.

In more details, the Applicant has found that, by introducing at least apredetermined amount of a liquid coolant into the grinding device so asto contact the rubber material during the advancing and grindingthereof, said coolant dissipates a part of the heat produced during thegrinding step and thus efficiently cools the rubber material while beingground.

Furthermore, in order to increase the grinding yield in fine particlesof the rubber material, the Applicant has found that at least onegrinding aid additive can be advantageously introduced into the grindingdevice.

In particular, the Applicant has found that a synergistic effect isobtained when at least one liquid coolant and one grinding aid additiveare introduced into the grinding device, said additive favourablysupporting the grinding operation. As a consequence of this synergisticeffect, the grinding yield in fine particles advantageously increases.

The Applicant believes that said favourable result is connected to thefact that: a) the grinding aid additives avoid the reagglomeration ofthe fine rubber particles produced during the process as well as theirsticking to the grinding device, and b) the grinding aid additivescontribute to the grinding action thanks to their hardness and/orabrasiveness. The present invention relates to a process for producing arubber powder from a vulcanized rubber material comprising the steps of:

-   -   feeding a grinding device with said vulcanized rubber material;    -   contacting said vulcanized rubber material with at least one        liquid coolant;    -   introducing at least one grinding aid additive into said        grinding device;    -   operating the grinding device so as to grind said vulcanized        rubber material to form said rubber powder, and    -   discharging said rubber powder from said grinding device.

The process according to the present invention further comprises thestep of introducing the liquid coolant into the grinding device.

Preferably, the grinding aid additive is introduced into the grindingdevice through at least one feeding inlet together with the vulcanizedrubber material.

Preferably, the introduction of the liquid coolant into the grindingdevice is carried out by means of at least one further feeding inletwhich is different from the feeding inlet of the vulcanized rubbermaterial and of the grinding aid additive.

Preferably, said at least one further feeding inlet is an injectionpoint for the liquid coolant.

Alternatively, the introduction of the liquid coolant into the grindingdevice is carried out by means of said at least one feeding inlet sothat the liquid coolant, the vulcanized rubber material and the grindingaid additive are fed into the extruder through the same feeding inlet.

According to an embodiment of the invention, the introduction of theliquid coolant into the grinding device is carried out by dripping.

According to a further embodiment, the step of contacting comprises thestep of wetting the vulcanized rubber material with the liquid coolantbefore the step of feeding.

According to a further embodiment, the step of contacting comprises thestep of impregnating the vulcanized rubber material with the liquidcoolant before the step of feeding.

According to the invention, when the liquid coolant introduced into thegrinding device contacts the rubber material during the grindingthereof, the coolant is able to remove the heat, or at least part of it,at the very beginning of its production so that a more efficient andeffective control of the rubber material temperature can be performedwith respect to the case in which a single external cooling, i.e. acooling carried out by means of a cooling circuit provided, forinstance, within the walls of the grinding device, is performed.

An example of grinding device according to the present invention is amill, e.g. a cutting mill, a refiner mill, a hammer mill, a grindingmill, a pin mill, a counter-rotating pin mill, a cage mill, a turbomill, or an attrition mill.

An alternative grinding device is an extruder.

A further alternative grinding device is a shredder or a granulator.

A further alternative grinding device is a Banbury mixer.

The process of the present invention is suitable for pulverizing anyvulcanized rubber materials, such as synthetic or natural polymers,copolymers, homopolymers, natural or synthetic rubber and mixturesthereof.

Preferably, the process of the present invention is suitable forpulverizing the vulcanized rubber material deriving from discardedtyres.

In case a discarded tyre is used, the latter is previously torn toshreds of remarkable size dimensions, for instance of about 3-5 cm insize.

Successively said shreds undergo a further size-reduction operation,which reduces the tyre pieces to chips for example of about 6-8 mm,while dedicated working operations are carried out in order to removesteel (e.g. by means of a magnetic separation) and textile material(e.g. by means of a pneumatic separation) from said chips. The reductionof the tyre shreds to tyre pieces of lower dimensions allows that nearly99% of the metallic material and a first amount of the textile materialare separated from the rubber material.

Successively, said chips are subjected to a pulverizing operation inaccordance with the present invention so as to obtain a rubber powder,the latter having an average dimension lower than 1 mm.

Alternatively, the discarded tyre torn to shreds (of about 50-100 mm) isdirectly fed into the grinding device (e.g. a grinding wheel mill) inwhich the pulverizing operation in accordance with the present inventionis carried out. According to said embodiment, part of the materialexiting from the grinding device is recycled thereinto in order toprovide for a further grinding of said material so as to further reducethe size thereof.

Successively, the rubber powder exiting from the grinding deviceundergoes a screening operation so as to separate the remaining amountof textile material from the rubber material.

The Applicant has found that the use of a grinding aid additiveadvantageously increases the sieving yield of the textile material fromthe rubber material at the end of the pulverization process.

In more details, the Applicant has found that by using a grinding aidadditive it is possible to efficiently and easily separate the textilematerial—i.e. the fibers—from the rubber powder, since the textilematerial tends to agglomerate and spontaneously separate by formingflakes upon the screens.

Therefore, during subsequent screening, the agglomerated fibers areretained on the screens and can be easily removed.

According to the present invention, the obtained rubber powder issubstantially devoid of the textile material and the waste of rubbermaterial is remarkably reduced with respect to traditional pulverizationprocesses wherein the textile material is separated, e.g. by means ofcyclone air separators, and a remarkable amount of rubber material cannot be recovered.

Preferably, the liquid coolant according to the present invention iswater.

More preferably, said liquid coolant is water at a temperature notgreater than 30° C. Even more preferably, said water is at a temperaturecomprised between 5° C. and 20° C.

Alternatively, the liquid coolant according to the present invention isan aqueous emulsion or suspension of at least one polymeric material,e.g. an elastomer (such natural rubber) or a resin.

Preferably, the liquid coolant is a non-cryogenic coolant.

Preferably, the liquid coolant is continuously fed to the grindingdevice.

The use of water as liquid coolant is particularly preferred not onlyfrom an economical and practical point of view, but also for the factthat the cooling action is particularly efficient because of waterevaporation. In fact, because of the heat production due to the grindingaction on the rubber material, the water introduced into the grindingdevice dissipates a part of the heat produced during said grindingaction and evaporates. Therefore, the rubber powder discharged from thegrinding device is substantially dry.

According to the present invention, the coolant is preferably introducedinto the grinding device in an amount not greater than 20% by weightwith respect to the amount of the rubber material. More preferably, thecoolant amount is not greater than 10% by weight with respect to theamount of the rubber material.

According to a further aspect of the present invention, the temperatureof the rubber material contained within the grinding device has to bemaintained below its melting or softening temperature so that the rubberparticles do not increase their tackiness during the grinding thereofand do not agglomerate.

In particular, the Applicant has perceived that the rubber materialintroduced into the grinding device and ground thereinto has to besuitably cooled by means of the liquid coolant mentioned above so that,at the exit of the grinding device, the temperature of the rubber powderis preferably not greater than 100° C., more preferably not greater than60° C.

Preferably, the grinding aid additives can be selected from: silica,silicates (e.g. talc, mica, clay), finely divided metal oxides orcarbonates (e.g. calcium carbonate, zinc oxide, magnesium oxide,alumina) and mixtures thereof.

According to the present invention, the grinding aid additive ispreferably introduced into the grinding device in an amount not greaterthan 20% by weight, more preferably from 0.5% to 10% by weight, withrespect to the amount of the rubber material.

According to an embodiment of the present invention, the grinding deviceis an extruder which comprises a barrel and at least one screw rotatablymounted into said barrel.

According to said embodiment, preferably the step of operating theextruder comprises at least one step of conveying the vulcanized rubbermaterial along the extruder and at least one step of grinding thevulcanized rubber material within the extruder.

Preferably, the step of contacting the rubber is carried out byintroducing the liquid coolant into the extruder barrel, saidintroduction being performed during at least one step of conveying thevulcanized rubber material along the extruder.

More preferably, the step of introducing the coolant into the extruderbarrel is performed in association with at least one step of grindingthe vulcanized rubber material within the extruder. More specifically,the step of introducing is performed during the step of grinding;alternatively, the step of introducing can be performed before the stepof grinding, or both before and during the step of grinding.

Generally, the extruder is provided with at least one feeding inlet forthe introduction thereinto of the rubber material previously reducedinto shreds.

Preferably, the extruder is provided with a main feeding hopper which islocated in correspondence of a first portion of the extruder screw.

According to an embodiment of the present invention, the rubber materialreduced into shreds is introduced into the extruder barrel by means ofsaid main feeding. hopper.

Preferably, the extruder is further provided with at least one furtherfeeding inlet, which is located in correspondence of a further portionof the extruder screw, at a predetermined distance from said mainfeeding hopper.

According to a further embodiment of the present invention, part of therubber material reduced into shreds is introduced into the extruderbarrel by means of said at least one further feeding inlet. According tosaid embodiment, said at least one further feeding inlet is a lateralfeeding inlet.

Preferably, the rubber material is continuously introduced into theextruder.

According to a preferred embodiment of the present invention, the liquidcoolant is fed to the extruder through said at least one further feedinginlet. Preferably, said at least one further feeding inlet is aninjection point of the liquid coolant to be introduced into theextruder.

Alternatively, the liquid coolant is fed to the extruder through said atleast one lateral feeding inlet. According to a further embodiment, theliquid coolant and the rubber material can be introduced together intosaid at least one lateral feeding inlet.

Alternatively, the liquid coolant is fed to the extruder through themain feeding hopper.

Generally, the extruder screw comprises a plurality of conveyingelements and kneading elements which are assembled according to apredetermined sequence, the latter depending on the kind of material tobe ground as well as on the grinding yield to be achieved. In moredetails, the conveying elements have the function of moving the rubbermaterial along the extruder barrel while the kneading elements have thefunction of grinding the rubber material, i.e. of transferring to therubber material the mechanical energy necessary for carrying out thedesired particle size reduction. Furthermore, the kneading elements havethe function of mixing the liquid coolant with the rubber material.

According to an embodiment of the present invention, the liquid coolantis preferably fed to the extruder through a further feeding inletpositioned in correspondence of at least one kneading element. Morepreferably, said further feeding inlet is an injection point.

According to a further embodiment of the present invention, the liquidcoolant is fed to the extruder through a further feeding inletpositioned in correspondence of a conveying element which is locatedimmediately upstream of a kneading element. This solution isparticularly preferred since the kneading element can be suitablycooled.

Therefore, the introduction of the liquid coolant in correspondence ofat least one kneading element or immediately upstream thereof is a veryadvantageous configuration since the liquid coolant is directlyintroduced into the extruder zones where the grinding step is performedand a heat amount is produced.

Furthermore, according to the present invention, it is also possible toselectively cool down only the kneading elements which, following totheir position along the longitudinal extension of the screw as well asto the specific rubber material to be pulverized, transfer to the rubbermaterial the highest mechanical shears and are the most effective in thegrinding action thereof.

Preferably, the liquid coolant is introduced into the extruder barrel byinjection through said at least one injection point.

Alternatively, the liquid coolant is introduced into the extruder bydripping. In that case, the liquid coolant is fed to the barrel by meansof the main feeding hopper and/or of at least one lateral feeding inlet.

Alternatively, the rubber material introduced into the extruder in theform of shreds of a predetermined granulometry is previously wet orimpregnated with the liquid coolant. This means that the step ofcontacting the vulcanized rubber material with the liquid coolant occursbefore the introduction of the rubber material into the extruder.

Preferably, the grinding aid additives are introduced into the extruderby means of said at least one further feeding inlet. More preferably,said additives are introduced into the extruder by means of said atleast one lateral feeding inlet.

Alternatively, said additives are introduced into the extruder by meansof said main feeding hopper together with the rubber material.

Preferably, said additives are introduced into the extruder by means ofa gravimetric metering device.

The process of the present invention allows that high grinding yields infine particles can be achieved in only one pass—i.e. without recyclingthe obtained rubber powder—while maintaining the process workingtemperature at a value remarkably higher than the working temperature ofthe liquid nitrogen. In other words, in only one pass, the process ofthe present invention allows to obtain grinding yields in fine particleswhich are comparable with those obtained with the cryogenic techniques,but with the advantage that the process of the present invention allowsimportant energy and cost savings, also in terms of apparatuses to beemployed.

Therefore, in only one pass, the process of the present invention allowsto obtain a grinding yield greater than 50% in particles having averagediameter lower than 600 μm (i.e. 30 mesh) and a grinding yield greaterthan 40% in particles having average diameter lower than 425 μm (i.e. 40mesh). Furthermore, a grinding yield greater than 20% in particleshaving average diameter lower than 200 μm can be obtained.

According to a further embodiment of the present invention, the processcomprises the step of sieving the rubber powder exiting from thegrinding device. Preferably, the rubber particles having averagediameter greater than 1 mm are recycled into the grinding device.

Therefore, according to said further embodiment, the process of thepresent invention further comprises the step of recycling at least apart of the rubber powder exiting from the grinding device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now further illustrated with reference to theattached figures, wherein:

FIG. 1 is a schematic diagram of a process according to the presentinvention wherein the grinding device is an extruder;

FIG. 2 is a graphic showing the influence of water on the grinding yieldof the vulcanized rubber powder obtained from the process according tothe present invention, and

FIG. 3 is a graphic showing the synergistic effect of water and silicaon the grinding yield of the vulcanized rubber powder.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically shows a plant 100 for producing a rubber powderfrom a vulcanized rubber material according to one embodiment of thepresent invention.

Plant 100 comprises an extruder 110 which is provided with at least onefeeding inlet.

In more details, according to the embodiment shown in FIG. 1, theextruder 110 comprises a main feeding hopper 111 a for the introductionof the vulcanized rubber material (see arrow A) to be ground intopowder.

According to said embodiment, the extruder 110 further comprises alateral feeding inlet 111 b and an injection point 111 c for theintroduction into the extruder of at least one grinding aid additive(see arrow B) and a liquid coolant (see arrow C) respectively.

The extruder according to the present invention can further comprise acooling circuit within the walls of the extruder barrel so that therubber material can be cooled down also from the outside, i.e. bycontacting the cooled barrel walls.

At the extruder end opposite to the main feeding hopper, the vulcanizedrubber powder is discharged from the extruder 110 as indicated by arrowD.

According to an embodiment (not shown) of the invention, the dischargedrubber powder is conveyed to at least one sieve so that part of thepowder can be recycled into the extruder, preferably into the mainfeeding hopper. Preferably, the rubber particles having average diametergreater than 1 mm are recycled.

Preferably, the extruder 110 is a co-rotating twin-screw extruder.

The vulcanized rubber material to be ground into a powder according tothe process of the present invention may comprise at least a natural orsynthetic diene elastomeric polymer, e.g. obtained by solutionpolymerization, emulsion polymerization or gas-phase polymerization ofone or more conjugated diolefins, optionally blended with at least onecomonomer selected from monovinylarenes and/or polar comonomers in anamount of not more than 60% by weight.

The conjugated diolefins generally contain from 4 to 12, preferably from4 to 8 carbon atoms, and may be selected, for example, from the groupcomprising: 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,1,3-pentadiene, 1,3-hexadiene, 3-butyl-1,3-octadiene,2-phenyl-1,3-butadiene, or mixtures thereof.

Monovinylarenes which may optionally be used as comonomers generallycontain from 8 to 20, preferably from 8 to 12 carbon atoms, and may beselected, for example, from: styrene; 1-vinylnaphthalene;2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl orarylalkyl derivatives of styrene such as, for example, α-methylstyrene,3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene,2-ethyl-4-benzylstyrene, 4-p-tolylstyrene and 4-(4-phenylbutyl)styrene,or mixtures thereof.

Polar comonomers which may optionally be used may be selected, forexample, from: vinylpyridine, vinylquinoline, acrylic and alkylacrylicacid esters, nitriles, or mixtures thereof, such as, for example, methylacrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate,acrylonitrile, or mixtures thereof.

Preferably, the diene elastomeric polymer may be selected, for example,from: cis-1,4-polyisoprene (natural or synthetic, preferably naturalrubber), 3,4-polyisoprene, poly(1,3-butadiene) (in particularpoly(1,3-butadiene) with a high 1,4-cis content), optionally halogenatedisoprene/isobutene copolymers, 1,3-butadiene/acrylonitrile copolymers,styrene/1,3-butadiene copolymers, styrene/isoprene/1,3-butadienecopolymers, styrene/1,3-butadiene/acrylonitrile copolymers, or mixturesthereof.

Alternatively, the vulcanized rubber material to be ground into a powderaccording to the process of the present invention may comprise at leastan elastomeric polymer which may be selected from elastomeric polymersof one or more monoolefins with an olefinic comonomer or derivativesthereof. The monoolefins may be selected from: ethylene and a-olefinsgenerally containing from 3 to 12 carbon atoms, such as, for example,propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or mixtures thereof.The following are preferred: copolymers between ethylene and anα-olefin, optionally with a diene; isobutene homopolymers or copolymersthereof with small amounts of a diene, which are optionally at leastpartially halogenated. The diene optionally present generally containsfrom 4 to 20 carbon atoms and is preferably selected from:1,3-butadiene, isoprene, 1,4-hexadiene, 1,4-cyclohexadiene,5-ethylidene-2-norbornene, 5-methylene-2-norbornene, vinylnorbornene, ormixtures thereof. Among these, the following are particularly preferred:ethylene/propylene copolymers (EPR) or ethylene/propylene/dienecopolymers (EPDM); polyisobutene; butyl rubbers; halobutyl rubbers, inparticular chlorobutyl or bromobutyl rubbers; or mixtures thereof.

The present invention is now further illustrated by the followingworking examples.

EXAMPLE 1 (COMPARATIVE)

The process was carried out by using a vulcanized rubber productproduced by Graneco s.r.l. (Ferrara—Italy). Said product was in the formof vulcanized rubber pellets having dimensions of between 2 and 5 mm andwas obtained from the grinding of truck tyres.

The pellets were fed to the main feeding hopper of a co-rotatingintermeshing twin-screw extruder having a cylinder diameter of 40 mm anda L/D ratio of 48.

The feeding flow of the vulcanized rubber pellets was set to 20 kg/h andthe screw rotation speed of the extruder was set to 300 rpm.

The temperature of the vulcanized rubber powder discharged from theextruder was measured by means of a thermocouple and a value of 56° C.was obtained.

Table 1 shows the grinding yield—expressed in percentage by weight withrespect to a total amount of 100 kg of rubber powder discharged from theextruder—with reference to different granulometric ranges of said rubberpowder.

In more details, the values of Table 1 have been obtained by sieving—fora period of time of about 6 minutes—the rubber powder discharged fromthe extruder by using a plurality of sieves of different sizes. Forexample, the value of 69.82% corresponds to the amount by weight ofrubber powder which had a particle size greater than 1000 μm and did notpass through the first sieve having size of 1000 μm, while, for example,the value of 6.86% corresponds to the amount by weight of rubber powderwhich had a particle size lower than 1000 μm but higher than 800 μm andremained on the sieve having size of 800 μm.

From the data reported in Table 1 it can be calculated that an amount ofonly 4.67% of the rubber powder discharged from the extruder had adimension lower than 400 μm, while an amount of only 13.68% of therubber powder had a dimension lower than 600 μm.

The data of Example 1 are plotted in FIG. 2 as indicated by curve “a”wherein in abscissa are reported the dimensions of the rubber powderwhile in ordinates is indicated the grinding yield expressed inpercentage.

EXAMPLE 2 (INVENTION)

The process was carried out by using the same vulcanized rubber productand the same twin-screw extruder described in Example 1.

The twin-screw extruder was operated at the same working conditions (interms of feeding flow and screw rotation speed) as disclosed in Example1.

The temperature of the vulcanized rubber powder discharged from theextruder was of 31° C. 4% of water—with respect to a total amount of 100kg of rubber powder discharged from the extruder—was continuouslyinjected into the extruder at a temperature of about 18° C. Said waterwas fed to the extruder by means of an injection pump and the injectionpoint was located at a distance of 14 diameters from the main hopper.

Table 1 shows the grinding yield—expressed in percentage by weight withrespect to a total amount of 100 kg of rubber powder discharged from theextruder—with reference to different granulometric ranges of said rubberpowder as described with reference to Example 1.

From the data reported in Table 1 it can be calculated that an amount of10.79% of the rubber powder discharged from the extruder had a dimensionlower than 400 μm, while an amount of 24.21% of the rubber powder had adimension lower than 600 μm.

Therefore, by comparing the data of Example 1 with the data of Example2, it can be observed that, thanks to the introduction of the water intothe extruder, the amount of rubber powder having dimensions greater than1000 μm decreased of about 16% (passing from 69.82% of Example 1 to52.61% of Example 2) and in Example 2, with respect to the correspondingvalues of Example 1, the amount of rubber powder having dimensions lowerthan 400 μm and lower than 600 μm was increased of about 6% and 10%respectively.

The data of Example 2 are plotted in FIG. 2 and indicated by curve “b”.

TABLE 1 Grinding yield (%) Example Example 1 2 Rubber >1000 69.82 52.61powder  800–1000 6.86 10.43 dimensions 600–800 9.63 12.75 (μm) 400–6009.01 13.42 300–400 3.66 8.35 200–300 0.95 2.40 100–200 0.05 0.05 <1000.00 0.00

EXAMPLE 3 (COMPARATIVE)

The process was carried out by using the same vulcanized rubber productand the same twin-screw extruder described in Example 1.

The feeding flow of the vulcanized rubber pellets was set to 40 kg/h andthe screw rotation speed of the extruder was set to 300 rpm.

The temperature of the vulcanized rubber powder discharged from theextruder was of 80° C.

Table 2 shows the grinding yield—expressed in percentage by weight withrespect to a total amount of 100 kg of rubber powder discharged from theextruder—with reference to different granulometric ranges of said rubberpowder.

From the data reported in Table 2 it can be calculated that an amount ofonly 54.4% of the rubber powder discharged from the extruder had adimension lower than 1000 μm, while an amount of 33.0% had a dimensionlower than 600 μm, an amount of 20.0% had a dimension lower than 420 μm,an amount of 14.8% had a dimension lower than 350 μm, an amount of 4.4%had a dimension lower than 200 μm, and an amount of 1.4% had a dimensionlower than 150 μm.

The data of Example 3 are plotted in FIG. 3 as indicated by curve “c”wherein in abscissa are reported the dimensions of the rubber powder,while in ordinates is indicated the grinding yield expressed inpercentage.

EXAMPLE 4 (COMPARATIVE)

The process was carried out by using the same vulcanized rubber productand the same twin-screw extruder described in Example 1.

The twin-screw extruder was operated at the same working conditions (interms of feeding flow and screw rotation speed) of Example 3.

The temperature of the vulcanized rubber powder discharged from theextruder was of 77° C.

A silica was used as a grinding aid additive and was introduced into theextruder through the main feeding hopper by means of a gravimetricmetering device. The silica amount was of 10% by weight with respect tothe amount of rubber material introduced into the extruder. The silicaused was Sipernat® 320 which is produced by Degussa and has specificsurface area of 175 m²/gr, mean particle size of 15 μm, Mohs hardness of7 and density of 2.65 g/cm³.

Table 2 shows the grinding yield—expressed in percentage by weight withrespect to a total amount of 100 kg of rubber powder discharged from theextruder—with reference to different granulometric ranges of said rubberpowder.

From the data reported in Table 2 it can be noted that, by comparing thedata of Example 3 with the data of Example 4, thanks to the introductionof the silica into the extruder, the amount of fine rubber powder hasincreased. For example, it can be noted that the use of the silica hasincreased the amount of the rubber powder of dimensions in the rangefrom 200 to 350 μm (from 10.40% of Example 3 to 12,60% of Example 4,i.e. with an increment of about 21%), the amount of the rubber powder ofdimensions in the range from 150 to 200 μm (from 3.00% of Example 3 to5.40% of Example 4, i.e. with an increment of about 80%), and the amountof the rubber powder of dimensions lower than 150 μm (from 1.40% ofExample 3 to 11,30% of Example 4, i.e. with an increment of about 700%).

From the data reported in Table 2 it can be calculated that an amount of63.5% of the rubber powder discharged from the extruder had a dimensionlower than 1000 μm, while an amount of 46.5% had a dimension lower than600 μm, an amount of 34.5% had a dimension lower than 420 μm, an amountof 29.3% had a dimension lower than 350 μm, an amount of 16.7% had adimension lower than 200 μm, and an amount of 11.3% had a dimensionlower than 150 μm.

The data of Example 4 are plotted in FIG. 3 and indicated by curve “d”.

EXAMPLE 5 (INVENTION)

The process was carried out by using the same vulcanized rubber productand the same twin-screw extruder described in Example 1.

The twin-screw extruder was operated at the same working conditions (interms of feeding flow and screw rotation speed) as disclosed in Example3.

The temperature of the vulcanized rubber powder discharged from theextruder was of 44μC.

A silica amount of 5% by weight—with respect to the amount of rubbermaterial introduced into the extruder—was fed to the extruder throughthe main feeding hopper thereof by means of a gravimetric meteringdevice. The silica used was Sipernat® 320 as described in Example 4.

Furthermore, a water amount of 5% by weight—with respect to the totalamount of rubber material—was continuously injected into the extruderthrough an injection point as described in Example 2. The water was at atemperature of about 18° C.

Table 2 shows the grinding yield—expressed in percentage by weight withrespect to a total amount of 100 kg of rubber powder discharged from theextruder—with reference to different granulometric ranges of said rubberpowder.

From the data reported in Table 2 it can be noted that, by comparing thedata of Example 4 with the data of Example 5, thanks to the introductioninto the extruder of 5% by weight of water in place of 5% by weight ofsilica (so that only 5% by weight of silica was used), the amount offine rubber powder has remarkably increased pointing out the synergisticeffect of silica and water. For example, it can be noted that the amountof the rubber powder of dimensions in the range from 200 to 350 μm hasincreased (from 12.6% of Example 4 to 13.4% of Example 5, i.e. with anincrement of about 6%), as well as the amount of the rubber powder ofdimensions in the range from 150 to 200 μm (from 5.4% of Example 4 to7.4% of Example 5, i.e. with an increment of about 37%), and the amountof the rubber powder of dimensions lower than 150 μm (from 11.3% ofExample 5 to 16.2% of Example 5, i.e. with an increment of about 43%).

From the data reported in Table 2 it can be calculated that an amount of64.2% of the rubber powder discharged from the extruder had a dimensionlower than 1000 μm, while an amount of 51.0% had a dimension lower than600 μm, an amount of 41.4% had a dimension lower than 420 μm, an amountof 37.0% had a dimension lower than 350 μm, an amount of 23.6% had adimension lower than 200 μm, and an amount of 16.2% had a dimensionlower than 150 μm.

Furthermore, by combining the data reported in Table 2, it can be notedthat the addition of water and silica to the rubber material allows toremarkably: increase the grinding yield in fine particles, i.e. inparticles having dimensions lower than 350 μm, preferably lower than 200μm.

The data of Example 4 are plotted in FIG. 3 and indicated by curve “e”.

TABLE 2 Example Example Example 3 4 5 Rubber >1000 45.40 36.40 35.60powder  600–1000 21.40 17.00 13.20 dimensions 420–600 13.00 12.00 9.60(μm) 350–420 5.20 5.20 4.40 200–350 10.40 12.60 13.40 200–150 3.00 5.407.40 <150 1.40 11.30 16.20

1. A process for producing a rubber powder from a vulcanized rubbermaterial comprising the steps of: feeding a grinding device with saidvulcanized rubber material; introducing at least one liquid coolant intosaid grinding device; contacting said vulcanized rubber material withsaid at least one liquid coolant; introducing at least one grinding aidadditive into said grinding device; operating the grinding device so asto grind said vulcanized rubber material to form said rubber powder; anddischarging said rubber powder from said grinding device.
 2. The processaccording to claim 1, wherein the grinding aid additive is introducedinto the grinding device through at least one feeding inlet togetherwith the vulcanized rubber material.
 3. The process according to claim1, wherein the introduction of the liquid coolant into the grindingdevice is carried out by means of at least one further feeding inlet. 4.The process according to claim 3, wherein said at least one furtherfeeding inlet is an injection point of the liquid coolant.
 5. Theprocess according to claim 1 or 2, wherein the introduction of theliquid coolant into the grinding device is carried out by means of saidat least one feeding inlet.
 6. The process according to claim 1, whereinthe introduction of the liquid coolant into the grinding device iscarried out by dripping.
 7. The process according to claim 1, furthercomprising the step of reducing the vulcanized rubber material intoshreds before the step of feeding.
 8. The process according to claim 7,further comprising the step of size reducing said shreds into chips ofdimensions lower than the dimensions of said shreds.
 9. The processaccording to claim 8, further comprising the step of separating metallicmaterial from the rubber material reduced into chips.
 10. The processaccording to claim 9, wherein the metallic material is separated bymeans of a magnetic separator.
 11. The process according to claim 8,further comprising the step of separating textile material from therubber material reduced into chips.
 12. The process according to claim1, further comprising the step of separating a remaining amount oftextile material from the rubber powder exiting from the grindingdevice.
 13. The process according to claim 11 or 12, wherein the textilematerial is separated by sieving.
 14. The process according to claim 1,wherein said rubber powder is sieved and then at least part of saidrubber powder is recycled.
 15. The process according to claim 1, whereinsaid liquid coolant is water.
 16. The process according to claim 15,wherein said water is at a temperature not greater than 30° C.
 17. Theprocess according to claim 16, wherein said temperature is not greaterthan 20° C.
 18. The process according to claim 1, wherein said liquidcoolant is an aqueous emulsion of at least one polymeric material. 19.The process according to claim 1, wherein said liquid coolant is anaqueous suspension of at least one polymeric material.
 20. The processaccording to claim 1, wherein said liquid coolant is introduced into thegrinding device in an amount not greater than 20% by weight with respectto the amount of said vulcanized rubber material.
 21. The processaccording to claim 20, wherein said amount is between 0.5% and 10% byweight with respect to the amount of the rubber material.
 22. Theprocess according to claim 1, wherein said at least one grinding aidadditive is selected from: silica, silicates, metal oxides, metalcarbonates, and mixtures thereof.
 23. The process according to claim 1,wherein said at least one grinding aid additive is introduced into thegrinding device in an amount not greater than 20% by weight with respectto the amount of said vulcanized rubber material.
 24. The processaccording to claim 23, wherein said amount is between 0.5% and 10% byweight with respect to the amount of the rubber material.
 25. Theprocess according to claim 1, wherein said grinding device is a mill.26. The process according to claim 1, wherein said grinding device is anextruder, said extruder comprising a barrel and at least one screwrotatably mounted into said barrel.
 27. The process according to claim1, wherein said grinding device is a shredder.
 28. The process accordingto claim 1, wherein said grinding device is a granulator.
 29. Theprocess according to claim 1, wherein said grinding device is a Banburymixer.
 30. The process according to claim 26, wherein the operation ofthe extruder comprises at least one step of conveying the vulcanizedrubber material along the extruder and at least one step of grinding thevulcanized rubber material within the extruder.
 31. The processaccording to claim 26, wherein the step of contacting the rubber iscarried out by introducing the liquid coolant into the extruder barrel.32. The process according to claim 30, wherein the step of introducingthe liquid coolant is performed during said at least one step ofconveying.
 33. The process according to claim 1 or 30, wherein the stepof introducing the liquid coolant is performed in association with saidat least one step of grinding.
 34. The process according to claim 1 or30, wherein the step of introducing the liquid coolant is performedduring said step of grinding.
 35. The process according to claim 1 or30, wherein the step of introducing the liquid coolant is performedbefore said step of grinding.
 36. The process according to claim 30,wherein the liquid coolant is introduced into said extruder through atleast one feeding inlet.
 37. The process according to claim 36, whereinsaid feeding inlet is a main feeding hopper.
 38. The process accordingto claim 36, wherein said feeding inlet is an injection point.
 39. Theprocess according to claim 36, wherein said feeding inlet is a lateralfeeding inlet.
 40. The process according to claim 38, wherein saidfeeding inlet is positioned in correspondence of at least one kneadingelement of said screw.
 41. The process according to claim 39, whereinsaid feeding inlet is positioned in correspondence of at least onekneading element of said screw.
 42. The process according to claim 38,wherein said feeding inlet is positioned in correspondence of aconveying element of said screw, said conveying element being positionedimmediately upstream of a kneading element of said screw.
 43. Theprocess according to claim 39, wherein said feeding inlet is positionedin correspondence of a conveying element of said screw, said conveyingelement being positioned immediately upstream of a kneading element ofsaid screw.
 44. The process according to claim 26, wherein said at leastone grinding aid additive is introduced into said extruder through atleast one feeding inlet.
 45. The process according to claim 44, whereinsaid feeding inlet is a main feeding hopper.
 46. The process accordingto claim 44, wherein said feeding inlet is a lateral feeding inlet. 47.The process according to claim 1, wherein the temperature of the rubberpowder discharged from the grinding device is not greater than 100° C.48. The process according to claim 47, wherein said temperature is notgreater than 60° C.
 49. The process according to claim 1, wherein saidvulcanized rubber material comprises at least one synthetic or naturalelastomeric polymer.
 50. The process according to claim 1, wherein saidvulcanized rubber material derives from discarded tyres.